Diphtheria-like illness found in Utah and Colorado pet owners

A diphtheria-like illness detected in Utah and Colorado is shedding light on how humans and pets exchange the bacterial infection, and how to treat it.

The big picture: In a report last week , the CDC announced that two cases, found in 2022 and 2023, were the first in the U.S. where pets and humans appear to have infected each other with C. ulcerans, a potentially harmful bacteria that hasn't been widely studied in humans.

• Corynebacterium ulcerans are more commonly found among animals — and can cause danger to wildlife and livestock, researchers in Japan wrote last year .

Zoom in: A northern Utah resident in 2022 complained of a leg wound that wouldn't heal. That patient, as well as their spouse, dog and three cats all eventually tested positive for the bacteria.

• A year later, a Colorado resident reported persistent upper respiratory problems. That patient as well as the dog of a visiting relative were infected.

The intrigue: The people and pets in the two states were given different antibiotics — and some turned out to be more effective than others.

• Erythromycin was the big winner, clearing up infections in the humans and animals alike.

How it works: C. ulcerans is similar to the bacteria that normally causes diphtheria — a highly contagious and often-serious disease that has been controlled in the U.S. by a vaccine. Diphtheria is spread through respiratory droplets or contact with sores.

• C. ulcerans also can lead to diphtheria, which includes symptoms like fever, sore throat, swelling and a gray coating in the nose or mouth, formed by dead tissue that was killed by a toxin that the bacteria produces.
• Infections of C. ulcerans are frequently asymptomatic but can become deadly if a sick patient goes untreated.

Zoom out: C. ulcerans, while uncommon, is considered an " emerging pathogen ," researchers wrote in 2019.

• Cases have gradually risen in recent decades in several countries — in people and animals .

Threat level: "We do know it is very rare and therefore not a major threat to humans," Mary Hill, epidemiology manager for the Salt Lake County Health Department, wrote in a statement to Axios.

The big picture: The two U.S. cases amount to a small data set, but they provide some clues to health officials as to how best to treat C. ulcerans: antibiotics, disinfecting surfaces and limited contact with others.

• "Prompt identification, treatment, and control" are needed to avoid potentially serious complications, researchers wrote.